I. Field of the Invention
The present development relates generally to stent or graft devices for implantation in an anatomical structure and, more particularly, to intravascular catheter deliverable branched stent or graft devices and methods of fabrication. Embodiments include unique branched stent or graft devices for the treatment of abdominal aortic aneurysms (AAA) involving the aorta-iliac bifurcation by reinforcing, excluding, bridging, or lining the diseased vessel, and to methods of fabrication of such as stent or graft devices involving a unique braiding technique using a single plurality of filaments to form two hinged legs and the common body or trunk portion of the device.
II. Related Art
An aortic aneurysm is a weak area in the wall of the aorta, the main blood vessel that carries blood from the heart to the rest of the body. The aorta extends upwards from the heart in the chest and then arches downwards, traveling through the chest (the thoracic aorta) and into the abdomen (the abdominal aorta). The normal diameter of the abdominal aorta is about one inch (2.5 cm).
Aortic aneurysms are frequently caused by the breakdown of the muscular layer and the elastic fibers within the wall of the aorta. The breakdown usually occurs over time, frequently in patients over 40 years of age, and can be caused by prolonged high blood pressure, effects from smoking or a genetic predisposition. As the vessel tissues deteriorate, the vessel wall strength decreases, and the high blood pressure causes the aortic wall to stretch beyond its normal size, forming an aneurysm. The weak aneurysm bulges like a balloon over time and can burst if the wall becomes too thin and weak to hold the blood pressure.
Most commonly, aortic aneurysms occur in the portion of the vessel below the renal artery origins. The aneurysm may extend into the aorta-iliac bifurcation and into the iliac arteries supplying the hips, pelvis and legs.
Once an aneurysm reaches 5 cm (about 2 in.) in diameter, it is usually considered necessary to treat to prevent rupture. Below 5 cm, the risk of the aneurysm rupturing is lower than the risk of conventional surgery in patients with normal surgical risks. The goal of therapy for aneurysms is to prevent them from rupturing. Once an AAA has ruptured, the chances of survival are low, with 80-90 percent of all ruptured aneurysms resulting in death. These deaths can be avoided if the aneurysm is detected and treated before it ruptures and ideally treated at an early stage (smaller aneurysm) with a lower risk procedure.
AAA can be diagnosed from their symptoms when they occur, but this is often too late. They are usually found on routine physical examination, through use of ultrasound, or by chest and abdominal X-rays. On examination, a doctor may feel a pulsating mass in the abdomen. If the doctor suspects an aneurysm, he/she will probably request that an ultrasound scan be carried out. Other scans, such as computerized tomography (CT) and magnetic resonance imaging (MRI) may also be performed. These scanning techniques are very useful for determining the exact position of the aneurysm.
The surgical procedure for treating AAA involves replacing the affected portion of the aorta with a synthetic graft, usually comprising a tube made out of an elastic material with properties very similar to that of a normal, healthy aorta. This major operation is usually quite successful with a mortality of between 2 and 5 percent. The risk of death from a ruptured AAA is about 50%, even during surgery.
More recently, instead of performing open surgery in undertaking aneurysm repair, vascular surgeons have installed an endovascular stent/graft delivered to the site of the aneurysm using elongated catheters that are threaded through the patient's blood vessels. Typically, the surgeon will make a small incision in the patient's groin area and then insert a delivery catheter containing a collapsed, self-expanding or balloon-expandable stent/graft to a location bridging the aneurysm, at which point the stent/graft is delivered out from the distal end of the delivery catheter and allowed or made to expand to approximately the normal diameter of the aorta at that location. The stent/graft, of course, is a tubular structure allowing blood flow through the lumen thereof and removing pressure from the aneurysm. Over time, the stent/graft becomes endothelialized and the space between the outer wall of the stent and the aneurysm ultimate fills with clotted blood. At this time, the aneurysm is no longer subjected to aortic pressures and thus will not continue to grow.
In treating AAAs that involve the aorta-iliac bifurcation, various stent or grafts designs have been placed to support, bridge or reline the vessels in the aneurysm segments. This has often involved multiple self expanding stents or stent grafts such as a large diameter stent or graft in the aortic segment and two smaller stents or grafts placed in each of the iliac arteries. In other designs the stent or graft has been designed to extend from the aortic segment into one branch of the iliac artery. In this case a hole is provided in the stent or graft to accommodate blood flow to the other iliac artery. A second stent or graft may be optionally placed into the other iliac artery and extending into the hole in the first stent or graft provided for iliac branch blood flow.
It has become apparent through use and clinical experience that the junctions of multiple stents or grafts presented placement problems of component alignment within the body. The stents or grafts being independent of each other caused components to rub against each other causing metal fatigue and flow discontinuities or thrombosis could occur where one component was not aligned with another and protruded into the blood flow. Use of multiple components also caused uneven vessel support such as where overlapping components may have an excess in vessel support as well as unsupported portions of the vessel where gaps occur between components. In the case of grafts, gaps between components cause leaks and may result in continued blood pressure exposure to the aneurysm.
As a result there remains a need for an alternative one piece stent or graft designs that covers the entire aneurysm segments including the main aortic segment as well as both iliac artery segments. It is also desirable that such a design be collapsible for percutaneous catheter delivery to the treatment site as well as self expandable when deployed from the delivery catheter.
U.S. Pat. No. 6,409,750 to Hyodoh et al. discloses woven bifurcated and trifurcated stents together with methods of fabrication. Those devices include a first plurality of wires defining a first leg having a first portion and a second plurality of wires defining a second leg having a second distal portion, and a common body having a distal end and a proximal portion, the common body being formed from at least the first and second plurality of wires, the proximal portion of the common body being adjacent to the distal portions of both legs, and both ends of at least one wire from both of the pluralities being located proximate the distal end of the common body. In this design the braided legs are connected only by the common body portion and gaps in metal coverage occur near the juncture of the legs.
U.S. Pat. No. 7,004,967 to Chouinard et al. describes a process for manufacturing a braided bifurcated stent. The process involves the use of two or more braiding machines in which a first discrete plurality of filaments are braided to form a first leg, and a second discrete plurality of filaments are braided to form a second leg. The process involves braiding the first plurality of filaments and the second plurality of filaments together to form the body using another braiding machine. That design results in metal coverage gaps occurring at the outside top portion of each leg and the process requires the use of multiple braiding machines. As with other concepts, the legs are not connected except to the common body portion. There are no common wires from one leg connecting to the other leg so a gap occurs between them.
There exists a need for a one piece branched stent or graft device that has improved metal coverage for uniform properties and a manufacturing process that is simple and produces a one piece design from a single discrete plurality of wires. There is a need for an improved bifurcated stent or graft that incorporates wires from one leg into the other leg creating a wire hinge and reinforcing the crotch area of the device. There is also a need for a device having the improved characteristics as above and which is also deliverable using a percutaneous intravascular catheter approach having a collapsed configuration for delivery through a catheter and a self expanding configuration when released from the catheter confines. The present development provides such a device.